1. Field of the Invention
The present invention relates to an injection molding method and injection molding apparatus particularly suitable for an elongated molded article, such as a resin part for a motor vehicle or the like.
2. Description of Related Art
An elongated resin product, for example, a protector for a wiring harness of the motor vehicle is generally manufactured by an injection molding machine. The injection molding machine has an injection unit for melting a resin material so as to inject, and a mold clamping unit for clamping a metal mold by a high pressure, and a capacity thereof is frequently expressed by a “mold clamping force.” The “mold clamping force” is expressed by a product of “projected area of a molded article in a surface perpendicular to a moving direction of the metal mold” and “average resin pressure within the metal mold.” The greater a value (expressed by ton) of the mold clamping force is, the larger the apparatus is. A cost of equipment is increased accordingly. For example, about 200 tons of mold clamping force is required even in an elongated resin product having a length of about some tens cm, it is desired to make the equipment compact by reducing the mold clamping force.
In order to reduce the mold clamping force, there has been employed mainly a method of making an injection pressure low (as a result, the average resin pressure within the metal mold becomes low). As the low pressure molding method mentioned above, there have been known a method of injecting a molten resin into a cavity of the metal mold under a half-open state and clamping the mold before solidification, a method of previously injecting a predetermined amount of molten resin into the cavity, intruding the molten resin charged in another sub chamber (a resin reservoir) into the cavity, and clamping the mold before solidification, and the like.
However, in these low pressure molding methods, since there still exists a need of making the molten resin to go around all over within the cavity, it is impossible to sufficiently lower the injection pressure (by extension, the average resin pressure within the metal mold), and there is a limit in lowering the mold clamping force.